There can be days, months, even years that you don't suffer from the symptoms of PTSD. I don't know what that feels like, yet, but I do know it is possible. The most I have gone is a day. My doctors and social workers have told me that this is possible and have also educated me on the simple fact that it will never truly go away. It can always come back, even if it has been gone for years. So, I guess it is lifelong but not persistently so in every case.